1. Field of the Invention
The present invention relates to a method and apparatus for monitoring lubricants in an engine. In particular, the present invention relates to monitoring the level and quality of a lubricant, such as oil, in an engine.
During use, engines, such as gas turbine engines, require lubrication. For example, lubrication may be required to reduce the wear of internal parts that move relative to each other and/or to reduce the friction between such components. Typically, therefore, an engine is provided with a lubrication system, which may comprise one or more pumps and ducts to deliver a lubricant to the desired position in the engine.
Any suitable lubricant may be used, such as oil. The oil/lubricant may contain various additives, such as stabilizers, which may be intended to improve performance of the oil (for example by further reducing friction between lubricated components and/or increasing the temperature range over which the lubricant is effective) and/or to increase the useful life of the lubricant.
2. Description of the Related Art
In order for the lubrication system to perform as intended, the amount (or volume) of lubricant in the system typically needs to be maintained at or above a certain level. Thus, during use, the oil level may be monitored. In some systems, this may be performed using an oil level probe that is inserted into a part of the lubrication system, such as a tank which contains some of the oil in the system.
An oil level probe may operate by supplying an alternating current (AC) to a set of electrodes that are at least partially submerged in the oil whose level is to be measured, and then calculating the capacitance between the electrodes. The capacitance between the electrodes is a function of the depth to which the electrodes are immersed in oil, because the dielectric strength of the oil is different to the dielectric strength of the gas surrounding the non-submerged portion of the electrodes. Thus, the oil level can be determined by the calculated capacitance between the electrodes to which the AC is supplied.
The quality of the lubricant is also important in ensuring that the lubrication system operates in the intended manner. In this regard, typically the lubricant may degrade over time. This may be due to, for example, degradation resulting from temperature cycles and/or from contamination from the parts being lubricated. Modern engines tend to use less oil than their predecessors, meaning that oil tends to remain in the lubrication system for longer periods of time, and thus may need to resist degradation for longer periods of time. Furthermore, some modern engines may run at higher temperatures than their predecessors, which may lead to an increase in the rate of degradation of the oil. As a result, it is advantageous to be able to monitor oil/lubricant quality, or degradation, in the lubrication system, as well as oil/lubricant level. Furthermore, it is desirable to be able to monitor the oil/lubricant quality (as well as level) remotely.